1. Field of the Invention
The present invention relates to a heat fixing unit for fixing an image on a sheet and more particularly to a heat fixing unit for fixing an image on a sheet with application of heat in an image forming apparatus such as a copying machine.
2. Description of the Related Art
It has been customary heretofore in an image forming apparatus such as a copying machine that a heat fixing unit is used for fixing a transferred image onto a sheet.
As shown in FIG. 5, this type of conventional heat fixing unit constitutes a single heater 40, a single temperature sensor 41 arranged in the vicinity of the heater 40, a crossflow fan 42 for blowing out hot air heat generated from the heater 40, a motor 43 for rotating the crossflow fan 42, and a casing 44 for housing the above devices therein in a state insulated from the exterior. The heat fixing unit controls the temperature of the heater 40 in accordance with the result detected by the temperature sensor 41 irrespective of the length of the heater 40.
In the related-art heat fixing unit, a difference in temperature is generated in the longitudinal direction of the heater because the heater is long and the heat leaks out to the exterior with a limitative heat resistance. The single temperature sensor cannot detect the distribution of temperature, thus resulting in nonuniformity of a temperature distribution as shown in FIG. 6.